NAME¶
gl_FrontFacing - indicates whether a primitive is front or back facing
DECLARATION¶
in bool gl_FrontFacing ;.SH "DESCRIPTION"
Available only in the fragment language,
gl_FrontFacing is an input
variable whose value is
true if the fragment belongs to a front-facing
primitive and false otherwise. The determination of whether a triangle
primitive is front-facing is made by examining the sign of the area of the
triangle, including a possible reversal of this sign as controlled by
glFrontFace. One way to compute this area is:
a=12 ∑ j=0 n-1 x w i y w i+1 - x w i+1 y w i
where x w i and y w i are the x and y window coordinates of the
ith
vertex of the n-vertex polygon.
The sign of this computation is negated when the value of
GL_CLIP_ORIGIN
(the clip volume origin, set with
glClipControl()) is
GL_UPPER_LEFT.
VERSION SUPPORT¶
|
OpenGL Shading Language Version |
|
|
|
|
|
|
|
|
|
|
|
Variable Name |
1.10 |
1.20 |
1.30 |
1.40 |
1.50 |
3.30 |
4.00 |
4.10 |
4.20 |
4.30 |
4.40 |
4.50 |
gl_FrontFacing |
✔ |
✔ |
✔ |
✔ |
✔ |
✔ |
✔ |
✔ |
✔ |
✔ |
✔ |
✔ |
SEE ALSO¶
gl_FragCoord(),
glClipControl()
COPYRIGHT¶
Copyright © 2011-2014 Khronos Group. This material may be distributed
subject to the terms and conditions set forth in the Open Publication License,
v 1.0, 8 June 1999.
http://opencontent.org/openpub/.
COPYRIGHT¶
Copyright © 2011-2014 Khronos Group